// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2014 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_SOLVEWITHGUESS_H
#define EIGEN_SOLVEWITHGUESS_H

namespace Eigen {

template <typename Decomposition, typename RhsType, typename GuessType> class SolveWithGuess;

/** \class SolveWithGuess
  * \ingroup IterativeLinearSolvers_Module
  *
  * \brief Pseudo expression representing a solving operation
  *
  * \tparam Decomposition the type of the matrix or decomposion object
  * \tparam Rhstype the type of the right-hand side
  *
  * This class represents an expression of A.solve(B)
  * and most of the time this is the only way it is used.
  *
  */
namespace internal {

    template <typename Decomposition, typename RhsType, typename GuessType>
    struct traits<SolveWithGuess<Decomposition, RhsType, GuessType>> : traits<Solve<Decomposition, RhsType>>
    {
    };

}  // namespace internal

template <typename Decomposition, typename RhsType, typename GuessType>
class SolveWithGuess
    : public internal::generic_xpr_base<SolveWithGuess<Decomposition, RhsType, GuessType>, MatrixXpr, typename internal::traits<RhsType>::StorageKind>::type
{
public:
    typedef typename internal::traits<SolveWithGuess>::Scalar Scalar;
    typedef typename internal::traits<SolveWithGuess>::PlainObject PlainObject;
    typedef
        typename internal::generic_xpr_base<SolveWithGuess<Decomposition, RhsType, GuessType>, MatrixXpr, typename internal::traits<RhsType>::StorageKind>::type
            Base;
    typedef typename internal::ref_selector<SolveWithGuess>::type Nested;

    SolveWithGuess(const Decomposition& dec, const RhsType& rhs, const GuessType& guess) : m_dec(dec), m_rhs(rhs), m_guess(guess) {}

    EIGEN_DEVICE_FUNC EIGEN_CONSTEXPR Index rows() const EIGEN_NOEXCEPT { return m_dec.cols(); }
    EIGEN_DEVICE_FUNC EIGEN_CONSTEXPR Index cols() const EIGEN_NOEXCEPT { return m_rhs.cols(); }

    EIGEN_DEVICE_FUNC const Decomposition& dec() const { return m_dec; }
    EIGEN_DEVICE_FUNC const RhsType& rhs() const { return m_rhs; }
    EIGEN_DEVICE_FUNC const GuessType& guess() const { return m_guess; }

protected:
    const Decomposition& m_dec;
    const RhsType& m_rhs;
    const GuessType& m_guess;

private:
    Scalar coeff(Index row, Index col) const;
    Scalar coeff(Index i) const;
};

namespace internal {

    // Evaluator of SolveWithGuess -> eval into a temporary
    template <typename Decomposition, typename RhsType, typename GuessType>
    struct evaluator<SolveWithGuess<Decomposition, RhsType, GuessType>>
        : public evaluator<typename SolveWithGuess<Decomposition, RhsType, GuessType>::PlainObject>
    {
        typedef SolveWithGuess<Decomposition, RhsType, GuessType> SolveType;
        typedef typename SolveType::PlainObject PlainObject;
        typedef evaluator<PlainObject> Base;

        evaluator(const SolveType& solve) : m_result(solve.rows(), solve.cols())
        {
            ::new (static_cast<Base*>(this)) Base(m_result);
            m_result = solve.guess();
            solve.dec()._solve_with_guess_impl(solve.rhs(), m_result);
        }

    protected:
        PlainObject m_result;
    };

    // Specialization for "dst = dec.solveWithGuess(rhs)"
    // NOTE we need to specialize it for Dense2Dense to avoid ambiguous specialization error and a Sparse2Sparse specialization must exist somewhere
    template <typename DstXprType, typename DecType, typename RhsType, typename GuessType, typename Scalar>
    struct Assignment<DstXprType, SolveWithGuess<DecType, RhsType, GuessType>, internal::assign_op<Scalar, Scalar>, Dense2Dense>
    {
        typedef SolveWithGuess<DecType, RhsType, GuessType> SrcXprType;
        static void run(DstXprType& dst, const SrcXprType& src, const internal::assign_op<Scalar, Scalar>&)
        {
            Index dstRows = src.rows();
            Index dstCols = src.cols();
            if ((dst.rows() != dstRows) || (dst.cols() != dstCols))
                dst.resize(dstRows, dstCols);

            dst = src.guess();
            src.dec()._solve_with_guess_impl(src.rhs(), dst /*, src.guess()*/);
        }
    };

}  // end namespace internal

}  // end namespace Eigen

#endif  // EIGEN_SOLVEWITHGUESS_H
